The present invention relates to a method of forming a radial tire and an apparatus therefor.
In manufacturing a radial tire, a tire manufacturing system (a tire manufacturing system used in carrying out the one-stage forming method) is used, which, as shown in FIG. 5, comprises an expandable belt-tread assembly forming drum a, a mount b rotatably supporting the drum a and having an expanding/contracting mechanism, a material supply device c for supplying components of the belt-tread assembly to the drum a, a carcass forming drum d which can be expanded/contracted to a cylindrical state and a toroidal state, a mount e which rotatably supports the drum d, has expanding/contracting means, and further has an approaching/leaving mechanism for adjusting a bead clearance, a material supply device f for supplying components, such as an inner liner, chafer, carcass ply, and sidewall, composing of a carcass to the drum d, a carrier g having an expandable holding claw which installs the belt-tread assembly to the outer periphery of a green carcass formed into a toroidal shape by the drum d by moving the assembly on the drum a to the position of the drum d while holding the assembly from the outside and removes a finished green tire from the drum d while holding the green tire from the outside and means which installs a left bead core to a predetermined position when the green tire is at the position of the drum d, a rail and drive device h for moving the carrier g, a pressing device i for appropriately pressing the assembly on the drum a, and a pressing device j for the belt-tread assembly delivered from the carrier g to the green carcass. For the above-described tire manufacturing system, Japanese Patent Provisional Publication No. 54-125277 (No. 125277/1979) should be referred to, if necessary.
In this tire manufacturing system, the drum a and the drum d are coaxially arranged so as to face each other. On the drum d,
(1) First, a sidewall SW is wound on the right and left portions composing the tire side wall and joined. PA1 (2) Then, cushion rubber CR and the like for protecting the tire in contact with the wheel portion when installed an the car is wound and joined. PA1 (3) Then, an inner liner rubber sheet IL is wound and joined. PA1 (4) Then, a rubber sheet (usually called a carcass ply CP) including fibers (in most cases, steel cords arranged in parallel in the axial direction of the drum d) is wound and joined. PA1 (5) Bead cores BC are arranged at the right and left symmetrically with respect to the center of the drum d at the outside of the above materials. FIG. 6 shows a state in which the process (5) is completed after the processes (1) to (4) have been carried out. PA1 (6) Then, the bead core lower part of the drum is expanded so that the material layer on the drum d is pressed against the inner peripheral portion of the bead core. FIG. 7 shows this state. PA1 (7) Then, compressed air is supplied while the clearance of the bead cores is decreased. After the material layer is formed into a toroidal shape, the material layer at the outer end portion of the bead core is folded back so as to wrap the bead core, and pressed against the toroidal material layer. PA1 (8) At an appropriate time during the above work, a belt-tread assembly, which has been assembled in advance, is placed at the center of both bead cores. The inner surface of the assembly is extended in a toroidal shape, and joined to the material layer. Finally, the assembly and the material layer are formed under pressure by using the pressing device to complete the tire. PA1 (1) A carcass ply is laminated on the outer periphery of an inner liner, which is formed into a cylindrical shape on the first band forming drum, to form a carcass band, and the first band forming drum and the first transfer holding a bead core in advance are relatively moved in a coaxial manner. After a bead core is located at a predetermined position on the outside of the carcass band, the carcass band is expanded and pressed against the inner peripheral surface of the bead core to form a first assembly, which is held by the first transfer. PA1 (2) Alternatively, a carcass ply is wound on the outer peripheral surface of the first band forming drum and formed into a cylindrical shape, and the first transfer holding a bead core in advance is relatively moved in a coaxial manner. After the bead core is located at a predetermined position on the outside of the carcass ply, the carcass ply is expanded and pressed against the inner peripheral surface of the bead core to form a 1--1 assembly, which is held by the first transfer. After an inner liner is formed into a cylindrical 1-2 assembly such that the outside diameter thereof is smaller than the inside diameter of the 1--1 assembly on the first band forming drum and the 1-2 assembly is located at a predetermined position on the inside of the second assembly, the inner liner is expanded and pressed against the inner surface of the 1--1 assembly held by the first transfer to form a first assembly. PA1 (3) Alternatively, a carcass ply, which is formed so that the outer peripheral length thereof is equal to the inner peripheral length of the bead core by the first band forming drum, is elastically deformed temporarily into a standing wave shape inward in the radial direction. Then, the first transfer holding the bead core in advance and the first band forming drum are relatively moved in a coaxial manner, and the bead core is located at a predetermined position on the outside of the carcass ply. After that, the elastic deformation of the carcass ply is eliminated, and the carcass ply is pressed against the inner peripheral surface of the bead core to form a 1--1 assembly, which is held by the first transfer. After an inner liner is formed into a cylindrical 1-2 assembly such that the outside diameter thereof is smaller than the inside diameter of the 1--1 assembly on the first band forming drum and the 1-2 assembly is located at a predetermined position on the inside of the second assembly, the inner liner is expanded and pressed against the inner surface of the 1--1 assembly held by the first transfer to form a first assembly. PA1 (4) During this time, on the second band forming drum, a sidewall, reinforcement band around the bead, and the like are joined in sequence and formed into a cylindrical shape to form a second assembly. PA1 (5) Then, the first transfer holding the first assembly and the second band forming drum are relatively moved in a coaxial manner. After the second assembly is located at a predetermined position in the first assembly, the second assembly is expanded and pressed against the first assembly to form a third assembly. PA1 (6) The first transfer and the shaping drum are moved, and the third assembly held by the first transfer is transferred to the shaping drum. Then, the shaping drum is expanded, and the bead holding portions are brought close to each other to perform toroidal shape. A belt-tread assembly (fourth assembly), which has been laminated in advance into a cylindrical shape on the belt drum, is transferred by the second transfer, and assembled to the third assembly at proper timing during shaping. Thus, the formation of a green tire is completed.
The drum d is made up of an elastic body for the purpose of the above processes (5), (6), and (7), so that the surface thereof is soft. In addition, the rubber material such as the sidewall wound on the surface of the drum d is of a long-base triangular shape in cross section. Therefore, when the inner liner rubber sheet and the carcass ply are wound, the material does not have a flat surface, but has an irregular surface as shown in FIG. 8.
For this reason, when an operator attempts to wind and join the inner liner rubber sheet and the carcass ply, it is very difficult to do the work. More specifically, it is very difficult to keep the joining lap uniform throughout the joined portion. As a result, the quality of the product tire becomes unstable and productivity decreases remarkably. Also, it is difficult to make the work automatic because the surface of the drum d, which is the base of winding, is unstable and irregular as described above.
In such a situation, the applicant has already proposed a forming method and apparatus in which, as shown in FIGS. 9 to 12, the inner liner IL and the carcass ply CP are affixed to each other into a cylindrical shape in advance on a band drum having a cylindrical outer peripheral surface to form a carcass band, which is transferred onto the green carcass forming drum d by means of a carcass transfer KT. In this case, because the sidewall SW is of a long-base triangular shape in section, the sidewall SW must be wound on the green carcass forming drum (also called a shaping drum) and must be joined manually into a cylindrical shape.
With this method, the sidewall SW is of a long-base triangular shape, so that when it is cut to a regular size, the length of the thinner portion tends to shrink as compared with the thicker portion and the cut surface has an acute angle in the base direction. Therefore, in joining the leading and trailing ends, it is necessary to expand the thinner portion and to bring the ends into contact so that the distance in the radial direction from the drum center is equal. Also, when the sidewall SW is formed into a toroidal shape, it is necessary to join the thicker portion under pressure enough to prevent it from coming off. However, since the outside diameter of the drum is not uniform in the axial direction, the above-described joining work on the shaping drum requires careful manual work performed by a skilled worker.
Also, it is difficult to make the joining work automatic because a supply device (servicer) for the members around the bead and a stitcher as well as a metal chafer lie around the green carcass forming drum d, so that a space for installing automatic joining device cannot be secured. For the above-described tire forming method, Japanese Patent Provisional Publication No. 59-70548 (No. 70548/1984) should be referred to, if necessary.